The long-range goals of the project are to understand the biomechanical basis for mechanical sensitivity of afferent neurons innervating joint capsulse. We wilsh to understand how joint capsules are deformed when a joint is loaded, and how this relates to activation of capsules mechanoreceptors. The specific aims of the project are to relate discharges of single afferents to the magnitude of components of capsule strain. Experiments will be done using intact capsule studied in situ, and isolated capsule studies in vitro. Experiments are planned in both knee and hip joints. In the proposed studies, discharge of mechanically sensitive receptors from joint capsules will be related to components of strain at the location of the receptor in the capsule. Regional strains will either be measured by placing an array of markers around the locus of a receptor and measuring displacements of the markers which result from loading the capsule, or stresses and strains will be computed with a finite element model of the capsule. Measurements of strain will be made by digitizing a television image of the markers, and using computer analysis of the images to determine displacements. The magnitude of components of plane strain will be computed from displacements using finite element theory. A finite element model of the capsule will be produced an used to predict specific conditions at the locus of receptors in the capsule. In order to implement the finite element model, we ar planning stress-strain-time studies of capsule material properties, to be undertaken in isolated strips of capsule. Patterns of deformation of the intact capsule will also be studied, and the finite element model will be used to predict the way loads are transmitted across the boundaries of and distributed within the capsule.